Aiming at energy-saving and mercury-free environmental requirements, LED technologies have become the most important lighting source applied in large-scale LCD panels or lighting apparatuses. Based on thermal consideration, the LED rated power below 1 Watt even lower than 0.1 Watt has been the major cell device applied in nowadays displays or lighting apparatuses. A large amount, hundreds even thousands, of LEDs are necessary to be arranged in an apparatus and their connections are mostly in serial and/or in parallel forms. However, the combination form and the power demand for LEDs are very closely related to each other in design consideration. Therefore, the power demand for operating LEDs is highly related to the arrangement of LEDs.
A very high voltage is required if a large amount of LEDs are merely serially connected in one string, where a much larger current is required if the LEDs are only connected in parallel strings. As a result, it is necessary for a power supply to be configured with very high (low) output voltage and with very low (high) current source if all LEDs are connected only in serial or in parallel.
In other words, improper combination may raise the difficulty of the power design for driving multiple LEDs (multi-LEDs). Moreover, a large amount of LEDs connected only in either serial or parallel form may increase the probability of failure when operating LED devices and raise the difficulty for designing power supplies, and causing thermal issues as well. In fact, the above-mentioned issues are difficult to be solved by simply biasing the multi-LEDs in a stable operation region. A preferred biasing strategy for such as transistor, diode, and even power LEDs, is to place the operating point around the intermediate portion of the power dissipation (PD) curve to gain excellent performance. However, most literatures focus only on the promotion of LED drive configurations and are lack of investigation on the mentioned issues, even the estimation of power need is also scarce and scattered.
Therefore, an advanced method for solving the above-mentioned issues is highly needed.